This invention relates to retrieval of a fiber optic cable that has become wedged during installation in a conduit.
Fiber optic cables have become a preferred transmission system for telecommunication and data communication. These cables are generally installed underground inside a conduit. The conduit is often laid in trenches and can extend a mile or more. The conduit generally has a smooth inside diameter throughout its length. Several methods exist for installing the fiber optic cable into the conduit.
U.S. Pat. No. 4,836,503 (1989) to Giroux and U.S. Pat. No. 5,029,816 (1991) to Langston all relate to the installation of fiber optic cable in conduit. The methods described in these patents has to do with pulling the cable through the conduit. Intermediate devices are described in these patents so as to divide the required pull force into incremental quantities along the length of the conduit so as to not exceed the strength of the fiber optic cable. This requires excavation to access the conduit in the trench, splicing of the conduit, and the associated labor involved, at each intermediate station.
Another method of installing the fiber optic cable in the conduit is using air pressure and air flow (sometimes referred to as air blown fiber (ABF)). A seal(s) is installed at the leading edge shuttle of the fiber optic cable. The shuttle provides a seal between the fiber optic cable and the inside diameter of the conduit. The shuttle is sometimes referred to as xe2x80x9cbirdxe2x80x9d or a xe2x80x9cparachutexe2x80x9d. If the conduit is pressurized upstream of the shuttle, force is applied to the cable by the air pressure which causes the cable to move relative to the conduit, and hence, the cable is installed in the conduit.
Yet another installation method is provided by an apparatus for grasping the fiber optic cable and pushing it into the conduit. This is sometimes referred to as xe2x80x9cjettingxe2x80x9d. This process is used in conjunction with the ABF process.
Thus the cable is pushed into and pulled through the conduit. This combination of cable installation techniques is in favored use.
One major concern, when using this push and pull method, is the remedy employed in the event that the shuttle and the trailing cable get wedged or stuck in the conduit. This can occur when there is too small a bend radius in the conduit, slightly deformed conduit, or just because the length of run is too long for the air blowing/ABF system. Radio transmitters have been designed to attach to the shuttle so that if the cable should get wedged or stuck in the conduit, the location of the shuttle can be determined by an appropriate signal locator. This remedy may be hampered by the location of adjacent utilities, such as gas, water, TV cable and electric wiring. The appropriate utility approvals must be obtained before any digging at the site can begin. Then, a trench must be opened, generally using a back hoe, to a depth of three to six feet. The conduit is then separated and the obstruction cleared. Sometimes the excavation site is then used to install an assist jetting machine and ABF to proceed with the installation of the fiber optic cable. The conduit is then repaired, and the trench back filled. Significant costs are associated with this remedy.
Accordingly, it is the object of the present invention to provide a simple, cost effective way to retrieve a fiber optic cable that has become wedged or stuck in a conduit during the installation process. The advantages are:
(a) no excavation of a trench is required to retrieve the stuck cable.
(b) the exact location of the cable shuttle that is wedged or stuck is not required.
(c) approval of the utilities is not required to open a trench.
(d) the manpower to perform the retrieval is minimal.
(e) heavy equipment for earth removal is not required.
Still further objects and advantages will become apparent from a consideration of the ensuing description.
In accordance with the present invention the retrieval method and mechanism comprises a projectile with an attached retrieval line, and a receiver attached to the shuttle of a fiber optic cable. If a shuttle becomes wedged in the conduit, the projectile is propelled by air pressure down the opposite end of the conduit and strikes the receiver. The projectile and receiver become latched together. Applying tension to the retrieval line serves to dislodge the shuttle and fiber optic cable from its wedged or stuck position.